The present invention relates to a membrane separation device including a washing apparatus and a membrane module including a spiral wound type membrane module used in a membrane separation device such as a microfiltration device, ultrafiltration device, or reverse osmosis membrane separation device.
As a membrane module used for a membrane separation device, there has been known a spiral wound type membrane module in which separation membranes are wound around the outer circumference of a water collection pipe.
FIG. 5 is a perspective view, partly exploded, showing a structure of a conventional spiral wound type membrane module.
A plurality of envelope-like membranes 2 are wound onto a water collection pipe 1 with mesh spacers 3 being put between the membranes.
The water collection pipe 1 is provided with a slit-like opening for allowing the communication between the outside and the inside of the pipe. The membranes 2 are each formed in an envelope shape, inside of the membrane communicating with the inside of the water collection pipe 1. Inserted into each envelope-like membrane 2 is an inside spacer 4 such as mesh-like spacer, for forming a channel inside the membrane, so that the inside of the envelope-like membrane (hereinafter, sometimes referred to as just "membrane") 2 constitutes a permeated water channel.
The opposite ends of a roll 5 of the membranes 2 are provided with a top ring 6 and an end ring 7 at its flanges and brine seals 8 are fitted around the top ring 6 and the end ring 7.
Feed water flows from the front end of the membrane roll 5 into a feed water channel between the membranes 2 and further flows in the longitudinal direction of the membrane roll 5. Nonpermeated water is outputted from the rear end of the membrane roll 5. While the water passes in the feed water channels, the water permeates through the membranes 2 and flows into the pipe 1 and is taken out from the rear end of the pipe 1 as permeated water.
When the membrane module is fouled, it is cleaned by flowing permeated washing liquid or cleaning agents containing water into the permeated washing channels or the feed washing channels reversely. However, the conventional membrane module has required a large volume of permeated washing liquid or cleaning agents.
The conventional spiral wound type membrane module shown in FIG. 5 has also the following defects:
1) The water collection pipe 1 must have larger diameter to obtain a great flux within the pipe 1. However, this also makes the diameter of the spiral wound type membrane module larger.
2) The permeated water flows in each membrane spirally to the water collection pipe 1, so that a flow resistance increases in the membrane. A flow resistance is also high around the slit-like openings through which the permeated water flows from the inside of the membrane into the water collection pipe.
3) A volume of the feed water flowing in the feed water channels decreases as the feed water flows to the outlet by permeation into the envelope-like membranes, and a flow velocity of the feed water becomes small in a downstream region of the feed water channels whereby the membranes are to be fouled therearound.